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https://issues.apache.org/jira/browse/CASSANDRA-7546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14116223#comment-14116223
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graham sanderson edited comment on CASSANDRA-7546 at 8/30/14 7:02 AM:
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I thought I'd attach an image of the correlation between the hint spikes and
the massive memory allocation. There is a chicken and egg thing here, but if a
node starts hinting heavily, it may become unresponsive causing a knock on
effect.
!young_gen_gc.png!
!hint_spikes.png!
Note on the yellow node, there was a period of about 500 seconds of young gen
GC, which equates to about 3TB of garbage
was (Author: graham sanderson):
I thought I'd attach an image of the correlation between the hint spikes and
the massive memory allocation. There is a chicken and egg thing here, but if a
node starts hinting heavily, it may become unresponsive causing a knock on
effect.
Note on the yellow node, there was a period of about 500 seconds of young gen
GC, which equates to about 3TB of garbage
> AtomicSortedColumns.addAllWithSizeDelta has a spin loop that allocates memory
> -----------------------------------------------------------------------------
>
> Key: CASSANDRA-7546
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7546
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: graham sanderson
> Assignee: graham sanderson
> Fix For: 2.1.1
>
> Attachments: 7546.20.txt, 7546.20_2.txt, 7546.20_3.txt,
> 7546.20_4.txt, 7546.20_5.txt, 7546.20_6.txt, 7546.20_7.txt, 7546.20_7b.txt,
> 7546.20_alt.txt, hint_spikes.png, suggestion1.txt, suggestion1_21.txt,
> young_gen_gc.png
>
>
> In order to preserve atomicity, this code attempts to read, clone/update,
> then CAS the state of the partition.
> Under heavy contention for updating a single partition this can cause some
> fairly staggering memory growth (the more cores on your machine the worst it
> gets).
> Whilst many usage patterns don't do highly concurrent updates to the same
> partition, hinting today, does, and in this case wild (order(s) of magnitude
> more than expected) memory allocation rates can be seen (especially when the
> updates being hinted are small updates to different partitions which can
> happen very fast on their own) - see CASSANDRA-7545
> It would be best to eliminate/reduce/limit the spinning memory allocation
> whilst not slowing down the very common un-contended case.
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